hi… dont know if you have cured your problem,but i had the same thing,tried all sorts but couldnt find fault until last week…On mine it was the front mounting bar that goes across the front of the cab…
The bar wears inside where the pins go in,that hold the airbags…All i did was drill and tap a hole to fit a grease ■■■■■■ in,where the mounting pin goes into the bar…u can see where it goes,because this part of the bar is bigger diameter…it has solved problem,until i feel like fitting a new bar…hope this helps.
You will have to release her eventually, somebody will hear her knocking.
Can anyone help me I drive a Daf XF & I’ve had a knocking noise comeing from under the floor it’s been in the fitters 5 times to have differnt things done along with this constant kn ocking but they cant find out what it is Iv’e had new cab mounts & it’s still there, has any one had the same thing & can tell me so I can tell the garage who can’t find it thanks Ted.
Tin of mushy peas in the fridge? 
bigvern1:
Tin of mushy peas in the fridge?
somehow, i think the man is looking for sensible answers.
if the cab mounts have been done then its more than likely to be the rubber mounts on the end of the cab tilt ram,
i,ve had a merc and a scania with the exact same noise you describe and doing the above cured both of them
Trukkertone:
bigvern1:
Tin of mushy peas in the fridge?somehow, i think the man is looking for sensible answers.
Was a sensible answer clever ■■■■…I had one under my floor knocking! 
bigvern1:
Trukkertone:
bigvern1:
Tin of mushy peas in the fridge?somehow, i think the man is looking for sensible answers.
Was a sensible answer clever ■■■■…I had one under my floor knocking!
please stop throwing stones
Ok…Because you asked nicely! 
ive only ever had that trouble with daf’s it knocks right under your feet.
chaversdad:
if the cab mounts have been done then its more than likely to be the rubber mounts on the end of the cab tilt ram,
Is the correct answer.
Cab mounts are a very common problem on DAF’s, followed by ram rubbers.
Ken.
Trukkertone:
bigvern1:
Trukkertone:
bigvern1:
Tin of mushy peas in the fridge?somehow, i think the man is looking for sensible answers.
Was a sensible answer clever ■■■■…I had one under my floor knocking!
please stop throwing stones
+1
Nah nah na nah nah! +1…Get you SAFP
it is the actuall bar that has worn away
new bushings will stop it for a while
recon 1 abt £500 new abt £1000
jessicas dad:
ive only ever had that trouble with daf’s it knocks right under your feet.
that depends on which layby you park overnight in JD 
IF you bought one of Spankys, it might be one of his oompa loompas stuck under there
bigvern1:
Nah nah na nah nah! +1…Get you SAFP
Bless her, +2
My Daf knocked from new , went back to garage , came back same , now just throws engine stop light
on if temp gauge goes over half way point .
I picked one up yesterday, stopped at Newport Pagnell for a break and it wouldn’t start afterwards. Fitter had to come out, put 25 litres of diesel in, uncrack the injectors and bleed it, even though the gauge was showing nearly a quarter of a tank. He said it’s a fairly regular problem.
It’s the cover on the engine take it off and it’s cured.
check the clearance between the front wings and the lower cab step mouldings. The lower cab step is adjustable on it’s mountings and it can foul the bottom edge of the front wing during the movement of the cab on its suspension. This can result in quite a loud knock. Unless your wings are painted it’s very hard to spot.
Cheers
Neilf